I largely agree with the Sheaim advice on the first page but I have a little different perspective (and few additional tips):
1. I slightly prefer Os-gabella to Tebryn. I build my game around summoning, and Tebryn's Arcane trait may seem like the better choice - however, for me the KEY to victory is getting Catacomb Libralis. If you do, and can get the Planar gates going, you should be getting a lot of Mobius Witches which can be the centerpoint of your magic based strategy.
I have to admit I like wonders. Some wonders I like for any civ (guild of Hammers, The Nexus, sometimes From of the Titan and the Great Lighthouse). For the Sheaim, I want to get Catacomb Libralis and the Soul Forge. Since Os-gabella is industrious, it is a little easier getting the wonders with her.
2. With either leader, you want to go 'deep' with summoning, since both leaders are summoners. The easist is death magic, since you get solid summons with affinity. Since you can only get so many liches and eaters of dreams, you want a solid level 2 summons. Fire is also a reasonable choice but I think death is better.
If you go deep with death, you can get the level 2 and 3 promotions for free, incluing the promotion to lich.
3. So with your palace, the soul forge, and say 2 or 3 other death nodes, catacomb libralis, you will get magic users and mobius witches to be able to summon powerhouse units for 2 turns that move two. Going deep with death won't cost as much as it does with other civs, since your mobius witches will get some of the other spells you may be missing by random selection, although if you really want one like enchantment it is a little risky. (Early you may need other nodes like enchantment for economic reasons.)
4. Since you don't need to use up promotions on taking the death spells, promotions can be used for combat. In the late game on a standard map you can have 20 Mobius witches and 10 - 15 mages and 8 Eaters and liches. This gives about 30-35 wraithes and spectres, which should be combat 7, with 4 or so strength promotons'; and since they wiill be sundered, if the AC is up in the 50 - 70 range they are truly a powerhouse.
5. I know some people say the Sheaim don't need to pump up the Armageddon Counter, I disagree. The units from the planar gates can be spectacular (especially in volume), and it will make those powerhouse spectres even stronger. When the AC gets to 50 you will be getting a lot of units for free and adding 25% strength.
6. I agree getting the planar gates early may be a mistake,the early game is tough. But you want them up and running in the middle game.
7. I like to attack in the late middle game, I'm a builder. Early, you can use an army of pyre zombies on defense. If you are attacked, you can use roads to get to the enemy first, and a stack of these guys can take anyone out.
8. I've assumed all along that you get the Ashen Veil. The Stigmata of the Unborn is quite good. Mardero is very good and can cast wither to go along with your spectres and pyre zombies. Needless to say having the veil pumps up the AC. If you get close to getting the apocalypse, then build non-living units like pyre zombies and diseased corpses.
9. If you get catacomb libralis, then you will be getting a lot of Mobius witches early (which is good). If you get the nexus, you will be getting minotaurs. These are good units to go with a summoned based army (and pyre zombies), you want good defensive units to hold cities. If you use sacrifice the weak, you will probalby get public baths (succubi) and gambling houses (revelers). The succubi are really quie good. With a stack of 7 of them, casting charm, you can stop almost any enemy army in its tracks. You can use them to defend the home country whne the SoD goes out to conquer. Revelers are a solid unit but I'm not crazy about them.
Manticores are powerhouses, as good a unit as any - but you have to build a grove to get them so they will likely be a specialty. carnivals give Chaos Marauders, not as good as the other units you can get, so don't get a carnival unless you really need it.
Best wishes,
Breunor